This application relates to electrochemical chemical test strips of the type commonly used in testing for blood glucose levels. The test strips are disposable and are combined with a reusable meter unit for applying power to electrodes within the strip and for displaying results.
Electrochemical test strips are known in the art. Because test strips may be used several times a day and because each test strip can only be used once, the strips need to be made as inexpensively as possible. On the other hand, because inaccurate monitoring of blood glucose can result in significant health consequences to a user, the test strips also need to be made with fairly strict manufacturing tolerances to provide the needed level of accuracy. Further, because monitoring is commonly done by individuals of varying age and varying levels of manual dexterity, rather than by trained health care professionals, the association of the strip with the meter needs to be easy to achieve in a correct manner.
In the art, there are commonly two basic electrode configurations: facing electrodes in which the electrodes for performing an electrochemical measurement are disposed on different substrates in a facing arrangement across a test cell, and side-by-side electrodes, in which the electrodes are both positioned on the common substrate surface within a test cell. From these electrodes, leads are extended to allow for electrical connection between the electrodes and the meter unit. The present application relates to electrochemical test strips with electrodes in a facing configuration.
U.S. Pat. No. 5,437,999 discloses test strips with electrodes in a facing configuration in which contact is made with the lead from one electrode (the one on the bottom of the test cell) from the top surface of the strip, while contact is made with the lead for the other electrode (the one on the top surface of the test cell) from the bottom surface of the test strip. U.S. patent application Ser. No. 2005/0258050 discloses another test strip configuration in which contacts are made from the top and the bottom. In both of these cases, the entire surface of the substrates is metallized to provide the electrode and its associated lead formed from a single material.
Notwithstanding the availability of designs for strip connectors in which the connectors are targeted from the top and bottom of the strip, in some circumstances (for example to allow use of the strip with preexisting meter units having connectors adapted for one-surface connection) it may be desirable to use facing electrodes but have both of the connectors on a single surface. U.S. Pat. No. 6,071,391 discloses a facing electrode test strip in which both leads are on one of the substrates. This is accomplished by the upper electrode being conducted to its lead parts through a hole in the adhesive and/or spacer layer between the top and bottom substrates. This approach involves several extra steps in manufacturing and additional difficulties in manufacturing, since a hole needs to be made in the adhesive/spacer layer in alignment with a separately patterned underlying conductive lead and an extension from the electrode, and a conductive material then needs to be filled into the hole to make contact between the electrode and the lead on the two surfaces. US Patent Publication No. 2005/0000808 discloses a test strip construction in which the spacer layer is formed as two separate parts with a gap running from one side of the test strip to the other. A lead is formed on one substrate with an electrode connector that extends across this gap to contact an electrode on the other substrate. This electrode can be printed on the entire interior surface, and this combined with the use of a spacer with two separate pieces instead of a hole means that the positioning of the electrode connector is only important in one direction (the length of the strip). This is an improvement over the two dimensional control required in the case of a hole, but it nevertheless increases the risk of manufacturing errors which can lead to unworkable test strips and therefore to increased cost per usable strip.